1. Field of the Invention
The present invention relates to particle detection. For illustrative purposes only, the preferred embodiment of the present invention will be described in relation to a smoke detection system, but the invention should not be considered to be limited to that exemplary use.
2. Discussion of the Related Art
Air sampling or aspirated smoke detection systems operate by drawing air samples through a sampling network, to a central high sensitivity particle detector. The sampling network typically includes one or more sample pipes with a number of air sample inlets in the form of sampling holes or sampling points located along the length of the pipe(s). In such an arrangement, a single detector may be fed with air originating from many distinct geographical locations at which the air sample inlets are located. Thus a single such detector can monitor for the presence of smoke at many distinct locations simultaneously.
One recognised difficulty with air sampling systems as described above is that they do not identify through which air inlet smoke enters the system. If the air inlet is known, the geographical location of the source of the smoke may be inferred. This allows investigation of the likely site of the fire including allowing a person to be directed to the location of the smoke, so that they may investigate and possibly intervene and prevent further growth of the fire, or shut down equipment in the area. Alternatively, an appropriate fire suppression system may be deployed in a localised way, limiting damage caused by the system, as well as expense.
There have been attempts to provide air sampling particle detection systems capable of determining the geographical location at which smoke is detected, for example Jax, ‘Method and Device for locating accumulations of pollutants’, U.S. Pat. No. 5,708,218 and Hekatron Vertriebs GmbH, ‘Verfahren and Vorrichtung zur Erkennung eines Brandes’, EP 1811478.
Each of these systems measures the elapsed time between two instants at which measurements are made to infer where along sampling pipe (i.e. through which sample inlet) the detected smoke entered the system. However, this inferential process is often unreliable.
The Jax system measures the elapsed time between detection of a first smoke level, and a second smoke level. The time between detection of a first, lower level of smoke, and a second, higher level of smoke indicates the distance along the collection line at which smoke entered the system. However, this process may be inaccurate. For example, systems employing this approach rely upon the actual level of smoke detected at the first point of entry remaining approximately constant for the period of time beginning from the point at which smoke is first detected until the contribution from the second point of entry can be reliably detected. More specifically, an increase in smoke level, such as that caused by a fire of growing size, may result in an inaccurate estimate of the geographical location from which air has been drawn.
In Hekatron, a first air-sampling detection unit detects the presence of smoke. Responsive to detection of smoke, a second air-sampling detection unit is engaged, the air sampling unit drawing air along the pipe network. The time elapsed between initial detection by the first air-sampling unit and detection by the second air-sampling unit is measured. Ideally, the time elapsed indicates the location from which smoke filled air has been drawn. To ensure accuracy, such a system requires the aspiration system to operate in a highly consistent manner, each time it is operated. However, this is difficult to achieve as various features influence the operation of the fall, e.g. degradation of the aspiration system over time and variations in operational and environmental conditions e.g. air density, or the constriction of sampling points by dirt over time, will change the airflow characteristics within the system, and make the inference of the smoke address based on elapsed time potentially unreliable.
In some schemes, airflow may be temporarily reversed, introducing clean air to the sampling network, before redrawing air for detection. The idea in such schemes is to flush substantially all smoke particles from the system, before redrawing air through the sampling network and measuring the delay before detecting smoke. In theory, a longer delay indicates that the particles entered the sampling network at a point farther from the detector. However, these schemes suffer a drawback in that during the phase that clean air is introduced to the sampling network, smoke particles within the monitored environment may be displaced in the area surrounding the air inlets, since clean air is being expelled from the inlets. When air is subsequently drawn through the system, there may be an additional delay before smoke particles are once again drawn into the inlet.
It is therefore an object of the present invention to provide a particle detection system that addresses at least some of the aforementioned disadvantages. An alternative object of the invention is to provide the public with a useful choice over known products.
Reference to any prior art in the specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in Australia or any other jurisdiction or that this prior art could reasonably be expected to be ascertained, understood and regarded as relevant by a person skilled in the art.